This invention relates to motor vehicles having a liquid-cooled drive engine and hydraulic power steering.
In conventional internal combustion engines, liquid cooling of the engine generally utilizes a liquid coolant mixture and a liquid pump is used to circulate the coolant. As a rule, such liquid-cooling arrangements include a thermostat-controlled bypass in a circuit leading to a liquid/air heat exchanger. In this way, the cooling action can be adjusted in accordance with the engine temperature. Until the engine becomes hot, the bypass in the circuit is open so that the coolant is bypassed from the heat exchanger and, therefore, is hardly cooled at all. At high coolant temperatures, the bypass is closed and, consequently, the coolant passes through the heat exchanger.
On the other hand, motor vehicles having conventional hydraulic power steering arrangements include another liquid circuit supplied with hydraulic oil and require another pump, which is usually a vane pump. In German Patent No. 31 27 476 and in European Patent Application No. 0 283 803, excess oil pumped by a power steering pump is used to drive other hydraulic components, such as servo-braking installations, anti-skid brake-slip installations (ABS), vehicle level-adjusting installations, and hydraulic arrangements for operating the fork of a forklift truck. Thus, in all of these cases, the hydraulic fluid supplied for the power steering arrangement is also supplied to other force-generating arrangements. It is furthermore known in such cases, as described, for example, in European Patent No. 0 268 173, to provide priority valves arranged to assure that the hydraulic power steering arrangement is supplied with hydraulic fluid in a preferential fashion.